A robot is an example of a controlled programmable device capable of executing mechanical or electrical tasks. Robots have replaced human in performing those repetitive and dangerous tasks which humans prefer not to do, or are unable to do due to size limitations or the extreme environments. Robotics deals with the design, construction, operation, and application of robots, as well as computer systems for their control, sensory feedback, and information processing.
Soft robotic technologies are appealing for locomotion, and for manipulation of fragile or irregularly shaped objects; their potential to bring new capabilities to the field of robotics stems from the compliant materials of which they are fabricated, the simplicity of their actuation, and their potential for low cost. Soft actuators have been fabricated from a variety of materials (polymers, elastomers, hydrogels, granules) and operate with several different modes of actuation, e.g., pneumatic, hydraulic, electric and chemical modes of actuation.
Pneumatically powered elastomeric actuators are appealing because these structures are light weight, inexpensive, easily fabricated, and provide linear or non-linear motion with simple inputs. One type of composite soft robotic actuators is based on a pneumatic network design that comprises mm-scale channels embedded in an extensible elastomeric layer with an inextensible layer made of either a stiffer elastomer or the same elastomer embedded with a fabric. See International Application No. PCT/US2011/061720, filed Nov. 21, 2011. Upon pressurization of a single inlet, the pneumatic network actuator bends, and provides motion analogous to several hard actuators connected in series. Bending of the serially connected pneumatic network actuators occur by the straining of the top wall of the chamber, allowing the inside walls to deflect away from each other at the interface of the inextensible layer (similar to a hinge).
Pneumatic actuators powered by compressed-air can generate complex motions, however, most of these motions have, thus far, been slow (on the order of seconds) to achieve their maximum amplitude. Rates of actuation are limited by the large changes in internal volume required to achieve the full range of motion of the actuator, and therefore by the rate at which low-pressure gas can be transported through the tube connecting the actuator to a gas source. Pneumatic networks (networks of small channels embedded in elastomeric structures that can be inflated with air) usually require significant changes in volume (ΔV/V>3) to achieve their full range of bending. This requirement for large ΔV/V limits the performance of soft actuators that use pneumatic networks in three ways: i) it requires the transfer of large volumes of gas for actuation, (and as a result, limits rates of actuation to low values), ii) it generates a change of volume of the actuator that is significant (and as a result, requires that the system have large volumes in which to operate), and iii) it imposes high strains on the material of which the pneumatic network is fabricated (and, as a result, shortens the operating lifespan of the pneumatic networks).
Improvements to soft robotic design are therefore needed.